Yes — from a strict Jain view, watching 18+ content is considered a serious lapse for a layperson, because it strongly increases kashāyas like kāma-rāga, attachment, and passions, and it harms inner purity.

For a householder (shrāvaka/shrāvikā), it is not treated like a monk’s total vow-breaking, but it is still a major impurity and a serious fault that should be firmly repented, stopped immediately, and purified through pratikraman, repentance, self-restraint, and renewed vows.

For a monk or nun, such conduct would be far more severe and incompatible with the strict ascetic code.

So the strictest answer is:

• For a layperson: serious impurity, requiring sincere repentance and purification.
• For an ascetic: gravely improper and unacceptable.
• Best Jain standard: avoid it completely, because it weakens chastity, restraint, and inner purity.